Olaparib is a phthalizinone compound developed as a poly(ADP-ribose) polymerase (PARP) inhibitor for use in treating cancers including ovarian, breast, and prostate cancers. Synthesis of olaparib and characterization of solids forms of the compound is disclosed in U.S. Pat. Nos. 8,247,416; 7,692,006; and 8,183,369. Specifically, U.S. Pat. No. 8,247,416 claims 4-[3-(4-cyclopropanecarbonyl-piperazine-1-carbonyl)-4-fluoro-benzyl]-2H-pthalazin-1-one (Compound A) substantially in crystalline form, and in particular in Form A. This patent also claims a method of synthesizing 4-[3-(4-cyclopropanecarbonyl-piperazine-1-carbonyl)-4-fluoro-benzyl]-2H-pthalazin-1-one from 2-fluoro-5-(4-oxo-3,4-dihydro-phthalazin-1-ylmethyl)-benzoic acid. U.S. Pat. No. 7,692,006 claims some methods of obtaining 4-[3-(4-cyclopropanecarbonyl-piperazine-1-carbonyl)-4-fluoro-benzyl]-2H-pthalazin-1-one (Compound A) as crystalline Form A. This patent also claims an intermediate of 2-fluoro-5-(4-oxo-3,4-dihydro-phthalazin-1-ylmethyl)-benzoic acid (ED) useful for preparing olaparib and a method of synthesizing the intermediate. As for U.S. Pat. No. 8,183,369, it is directed to 4-[3-(4-cyclopropanecarbonyl-piperazine-1-carbonyl)-4-fluoro-benzyl]-2H-pthalazin-1-one as crystalline From L and a method of obtaining it from 4-[3-(4-cyclopropanecarbonyl-piperazine-1-carbonyl)-4-fluoro-benzyl]-2H-pthalazin-1-one Form A. Olaparib has been approved by the U.S. Food and Drug Administration for treatment of women with advanced ovarian cancer associated with defective BRCA genes. New solid forms of olaparib are needed for enhancing the compound's demonstrated efficacy in the treatment of such cancers, as well as for improving processes for manufacture of pharmaceutical formulations that contain the drug. The present invention meets this need, providing novel crystalline forms of olaparib and processes for preparing the crystalline forms.